1. Field of the Invention
The present invention relates to a “fastening socket”, which is a tool for tightening a bolt or a nut of a fastener, etc. used to fasten members in steel structures, machine frames, etc., to a “washer for receiving counter torque” used for fastening, and to a preferred “fastener” for fastening using the fastening socket and the washer for receiving counter torque.
2. Description of the Related Art
In steel structures such as bridges, etc., a plurality of members is fastened with bolts and nuts. In recent years, “torque wrenches”, which can control rotary torque such that tensile stress acting on a bolt is at a predetermined value after the fastening is completed, are used for such fastening.
An electrical powered torque wrench which is one of the torque wrenches is used (see Japanese Laid-Open Patent Application Publication No. 2008-110414). The electrical powered torque wrench (hereinafter, called an “electrical tool”) has a socket with a hexagonal hole, which is to be set on a nut or a bolt head. The socket is attached to a rotary shaft of the electrical tool. The electrical tool is provided with a rod member that is attached to a non-rotating part and serves to receive counter torque generated due to rotation of the nut (or the bolt). During tightening, the rod member attached to the electrical tool may be engaged with a member of a structure located near a fastening site, thereby preventing counter-torque from acting on an operator who is holding the electrical tool. The term “electrical tool” is used in the present specification and the claims for the sake of convenience and is not limited to electrically powered tools, and also refers to pneumatically powered tools and hydraulically powered tools.
If there is no such a member with which the rod member can be engaged, the operator has to hold the rod member to receive the counter-torque.
To solve this problem, there is provided a washer for receiving counter torque, which is to be located adjacent to a nut or a bolt for receiving such counter torque up to a predetermined torque during tightening, and a coaxial double socket for the washer (see Japanese Laid-Open Patent Application Publication No. SHO 50-18852). The present applicant filed an application for design registration for a washer having a shape similar in plan view to the above washer; the application was already registered (Japanese Registered Design No. 909618).
The coaxial double socket has an inner socket portion for engaging a nut (or a bolt head) that is disposed inside an outer socket portion for engaging a washer. The nut (or the bolt head) is non-circular such as hexagonal as seen in plan view, and the washer is also non-circular. Accordingly, before starting of tightening, positioning of the socket with respect to both of the nut (or the bolt head) and the washer in a rotational direction is required. Furthermore, since the inner socket portion and the outer socket portion are coupled with a gear mechanism, their positions are not free and dependent from each other. Furthermore, setting of their positions must be performed inside the socket, where an operator is not able to see. For these reasons, the positioning of them is very difficult to perform, particularly in a bad foothold or in a narrow space. As a result, workability is remarkably worsened. Furthermore, if the electrical tool is operated while the inner socket portion is engaged with the nut (or the bolt head) without positioning of the outer socket portion with respect to the washer, the washer or the outer socket portion may be damaged.
In the meanwhile, when a nut or a bolt head is rotated for fastening using the electrical tool, the nut may be relatively and simultaneously “rotated with” the bolt. In this case, it is necessary to fix the bolt head (or the nut), which is otherwise “rotated simultaneously”, using a spanner or the like. When a nut is threaded onto a bolt that is already penetrated through a dividing wall, for example, while one worker is turning the nut located on a front surface side of the wall using a torque wrench, another worker needs to fix a bolt head located on a rear surface side of the wall.
In such a case, a pair of two workers is always required. And, because of these two workers are not able to see each other, they must work together, checking each other's progresses on the bolt and the nut. The work under such a condition is extremely inefficient.